This application claims the priority of German patent document 100 05 415.3, filed Feb. 8, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a fibrous-structure electrode framework web strip, electrode plates produced therefrom and a process for producing a fibrous-structure electrode framework web strip.
For about 17 years, a new type of electrode frameworks has been in use industrially in the field of electrode technology for alkaline and acid storage batteries, namely the fibrous-structure electrode type. Fibrous-structure electrodes are distinguished by the fact that, unlike, for example, sintered electrodes, pocket-plate electrodes or even lead-grid electrodes, to hold the active compound they have a porous framework for the current discharge and fixing the active compound, instead of purely metallic holding or conductor elements. The porous framework is produced by chemical and subsequent electrodeposition metallization of a nonconductive plastic substrate of fibrous structure.
Storage batteries for storing electrical energy in the form of chemical energy which can then be extracted again as electrical energy were known as long ago as the end of the nineteenth century. Even today, the lead storage battery is in widespread use. In this battery, the electrodes or plates consist of the active material, which is the actual energy store, and a lead support (grid) which accommodates the active material. For some time, there have been storage batteries with a new type of electrode in which the framework has a fibrous structure. There is extensive known prior art for this type of electrode.
For example, German patent document DE-C 40 04 106 describes a metallized plastics-fiber electrode framework based on a nonwoven for battery electrodes with increased load-bearing capacity. German patent documents DE-C 36 31 055, DE-C 36 37 130, DE-C 38 43 903, DE-C 39 25 232, DE-C 41 06 696, DE-C 40 33 518, DE-C 42 42 443, and DE-C 196 27 413 have described the activation and chemical metallization and suitable processes, and German patent document DE-C 42 16 966 has described a process and an apparatus for the electroplating of nonwoven and needled-felt webs. The fundamentals of the electrodeposition of metal are described, by way of example, in Dettner-Elze: Handbuch der Galvanotechnik, Volume I/1, pp. 136 ff., C. Hanser Verlag Munich (1963) und in xe2x80x9cDie galvanische Vernickelungxe2x80x9d [The Electrodeposition of Nickel], from Galvanotechnik, editor: Professor Robert Weiner; Eugen G. Leuze Verlag, Saulgau/Wxc3xcrttemberg.
German patent documents DE-C 38 17 817, DE-C 38 17 826, DE-C 40 10 811 and DE-C 42 35 884 specify aqueous nickel hydroxide and/or cadmium oxide pastes for the vibratory filling of foam- and fibrous-structure electrode frameworks.
German patent document DE-C 38 22 209 has disclosed a device for the vibratory filling of porous electrode frameworks, and German patent document DE-C 38 22 197 has disclosed a process for the quasi-continuous filling, and German patent document DE-C 38 16 232 a process for the vibratory filling, of foam- or fibrous-structure electrode frameworks. German patent document DE-C 38 22 197 also includes cleaning excess paste off the electrode framework after the mechanical impregnation, preferably using brushes. German patent document DE-C 40 18 486 has disclosed a process for the production of fibrous-structure electrodes in which the framework, which has been calibrated prior to the mechanical impregnation, is calibrated again after the filling operation by being compressed over its entire surface. German patent documents DE-C 40 40 017 and DE-C 41 03 546 each describe a process for filling fibrous-structure electrode frameworks provided with current discharge lugs for storage batteries containing an active-compound paste with simultaneous calibration of the framework, in which in the first case the framework is rolled during the filling operation and in the second case the framework is pressed during the filling operation.
The technical teaching relating to the welding of current discharge lugs of various designs to a fibrous-structure electrode framework of the type described is listed in the German patent documents DE-C 42 25 708, DE-C 41 04 865, DE-C 39 35 368, DE-C 36 32 352, DE-C 36 32 351, DE-C 31 42 091.
The above compilation, which in no way claims to be complete, shows that fibrous-structure electrode technology is a field which is currently the subject of intensive work. In practice, there are nevertheless constantly recurring difficulties and inadequacies during the production of fibrous-structure electrode frameworks, in particular relating to the process steps of activation, metallization, reinforcement by electrodeposition, filling with active compound and cleaning off the excess paste after the filling operation. Such difficulties and inadequacies may have an adverse effect during assembly of the filled, dried fibrous-structure electrodes, the unfilled nickel-fiber frameworks in the case of FNC recom cells and the separators in the case of gastight or open Ni/Cd cells of narrow design. On the other hand, such adverse effects may emerge only when the cells are operating, on account of the constantly changing volume work of the electrodes (primarily the positive electrodes in this system) resulting from the charging and discharging, so that, for example, the separators fitted are in certain zones exposed to excessive loads.
The activation and the subsequent metallization of plastics-fiber frameworks and the subsequent electrodeposition surface treatment of the various substrates are by now sufficiently well known. The technique involving deposition of metal alloys or of individual metals on the surface of substrates is used primarily if the layer which is to be electrodeposited is to impart certain properties, such as electrical conductivity, shine, reflectivity, chemical resistance, etc., to the treated substrate which the substrate itself does not have to a sufficient extent.
Now that, in practice, an ever increasing range of substrates made from plastic fibers is being used for a very wide range of applications, an electrodeposition surface treatment has become customary for these substrates as well, not only for substrates which themselves have metallic properties. For this purpose, the electrically nonconductive plastics surfaces are initially xe2x80x9cactivatedxe2x80x9d by the deposition of a catalytically active substance, and are then xe2x80x9cmetallizedxe2x80x9d by chemical means. Therefore, the electrically nonconductive plastics surfaces are provided with a metallic coating which is then suitably reinforced by electrodeposition of the same metal and/or a different metal. The application of the above technology to textile woven fabrics, nonwovens, needled felts or open-pore foams has opened up completely new application areas for these materials.
The subsequent electrodeposition surface treatment of metallized substrates has hitherto been carried out in such a way that the substrate which is to be electroplated, in a plurality of strips arranged above one another, is applied to a plurality of electroplating stands arranged next to one anotherxe2x80x94spatially close togetherxe2x80x94and the electroplating frame is clamped in place by the movable upper parts. The substrate is connected to the electroplating stand with sufficient electrical conductivity. Other than at the contact points with the substrate, the electroplating stand has an insulating layer over the rest of its surface. In this arrangement, an electroplating stand is fitted with a plurality of substrate strips and, at the same time, a plurality of electroplating stands next to one another in one electroplating tank are fitted with continuous premetallized substrate strips.
After the immersion of the electroplating stands which bear the substrate webs and after the electroplating process, metallized fibrous-structure framework strips are then formed. To obtain a reinforced edge, as is described in principle in German patent document DE-C 31 42 091, for the subsequent welding of current discharge lugs onto the rigid metallized fibrous-structure framework strips, it is known from German patent document DE-C 42 16 966 (also visible from FIGS. 1 and 2) that a sufficient clear spacing of approximately 80 mm to 100 mm from the next substrate web or from the transverse reinforcements of the electroplating stands must be maintained at those edges of the inserted premetallized substrate webs at which reinforced edges are subsequently to be formed during the electroplating process.
It can also be seen from the abovementioned figures that, to achieve optimal utilization of the height of the electroplating tank, the frame stands are supplied in such a way that an upper part of the frame stands holds a substrate web which is twice as wide as that in the lower part of the frame stands. As a result of the clear distances described, a reinforced edge is formed on the upper clamped-in substrate web at both the upper edge and the lower edge, while on the lower clamped-in substrate web, which is only half the height of the upper substrate web, a reinforced edge is formed only on the lower edge, since transverse struts of the electroplating frame stands are situated directly against its upper side. As a result of the spaces, the free edges of the fibrous-structure electrode framework webs are metallized more intensively, the textile felt web thickness being widened in these regions as a result of a high level of metal being deposited. After the electroplating, the frame stands are removed from the electrolyte in the electroplating tank, washed in a dedicated station and mechanically separated into individual plates. As a result, twice as many individual plates are formed from the upper substrate web as from the lower substrate web of the example described above.
German patent document DE-C 42 16 966 discloses that, after the fibrous-structure framework strips have been mechanically separated into individual plates, fibrous-structure framework electrode blanks are formed; the edge of such blanks that has a high level of nickel is not at right angles to those sides of the blanks which have been sawn, cut or machined in some other way. Thus, considerable effort is required to clamp the activated and chemically metallized fibrous-structure framework webs into holding frames which are arranged in addition to the electroplating stands and are equipped with inner and outer needle strips that have provided needles in portions thereof. Only with such considerable effort is it possible for the edge having a high level of nickel to be inserted, and clamped by the outer, rotatable needle strips, in such a way that the upper and lower edges of the fibrous-structure webs run in a straight line prior to and during the electroplating, such that the structure webs do not exhibit any irregularities in the web. As a result, after the mechanical separation of the fibrous-structure framework strips into individual plates, it is possible to obtain fibrous-structure framework electrode blanks, of which the edge that has a high nickel level is at right angles to the sides of the blanks which have been sawn, cut or machined in some other way. In this type of design of a reinforced edge, nickel agglomerates (so-called xe2x80x9cdendritesxe2x80x9d), are formed at marked locations on the premetallized substrate web, inter alia at the fiber ends or individual projecting fiber tips. The size of these undesired dendrites is dependent on the operating program of the electroplating (increasing the current, current level), which in turn is dependent on the nickel level to be achieved in the fibrous-structure electrode (low, medium, high or extra-high load cell types). In some cases, however, they may extend in the longitudinal direction up to 8 mm to 10 mm, with maximum cross section of up to 5 mm.
In the second column, lines 41 to 43, German patent document DE-C 42 16 966 states that these dendrites are removed from the fibrous-structure electrode blanks in a subsequent production step. Their mass is therefore missing from the overall balance for the mean nickel level in the electrode. The application of nickel to the fibrous-structure electrode is not uniform over the entire electrode height. In the region of the lug attachment, an area of the reinforced edge extending at most approximately 3 mm over the electrode height, has a nickel level which is about three times that which exists on average over the entire electrode. Therefore, the reinforced edge of the framework is the most dimensionally stable part. After the fibrous-structure electrode blanks have been cut to size, they are welded to the current discharge lugs.
During manufacture, it has often turned out that, in a first operation the portion of the dendrites (which grow in the shape of a mushroom over the entire length of the upper edge), that projects over the front principal face of the fibrous-structure electrode framework is ground off; and in a second operation that portion which projects over the back principal surface of the fibrous-structure electrode framework is ground off. To improve handling of the fibrous-structure framework from a technical standpoint, during these working steps some of the dendrites which project over the upper side along the length of the edge are also included, since in the two working steps mentioned the operator inclines the fibrous-structure framework individually more or less steeply when passing through the length of the upper fibrous-structure framework edge while grinding off dendrites. In some cases, a further working step is performed, in which the residual portion of dendrites that project beyond the upper side along the length of the reinforced edge of the fibrous-structure electrode framework is also ground off. This working step depends heavily on having a skilled and reliable operator with a good eye for his work, since every inherently inhomogenous edge which is to be machined is of a different nature.
In order to avoid excessive removal of material from the reinforced edge at local areas along the length of the reinforced edge, work is generally performed in such a way as to err on the side of leaving too much material in place. That is, in recesses along the length of the reinforced edge, some of the dendrites are left in place, even up to a height of 2 to 3 mm. Also, at elevated sections along the length of the reinforced edge, the dendrites are left in place up to a height of from 0.2 mm to 0.5 mm.
If a circular indexing machine is used together with an associated welding unit to weld current discharge lugs onto fibrous-structure electrode frameworks that have been pretreated in this way (and have been cut to size in terms of width), in order to locate the fibrous-structure electrode framework on the inserted current discharge lug prior to welding, a region of the upper edge of the fibrous-structure electrode framework which is to be welded has to be used for positioning. If residues of dendrites are present in this region for the stop or if there are no residues of dendrites at other frameworks, during the welding operation the upper edge of the fibrous-structure electrode framework comes to lie farther up or down on the current discharge lug. As a result, the optimum positioning of the framework on the bevelled face of the current discharge lug, or the bevelled faces of the teeth of the current discharge lug, is influenced; therefore weld joints with scattered strength values are formed.
For optimum welding, the upper welding electrode or the mount for the fibrous-structure electrode frameworks on the turntable would have to be readjusted according to the form of the upper, machined edge of the fibrous-structure electrode framework. To obtain accurately dimensioned fibrous-structure electrodes, for the reasons mentioned above, the lower edge of the fibrous-structure electrode is cut only in a further operation following welding, in order to ensure that the entire height of the fibrous-structure electrode, including the welded-on current discharge lug, lies within the specified dimensional tolerances.
Furthermore, if the dendrites are not machined off in a separate operation, experience has shown that during the welding of the fibrous-structure electrode framework to the current discharge lug it is impossible for all the dendrites on the reinforced edge of the electrode framework to be included. Unwelded dendrites, however, may lead to disruptive short circuits, possibly even causing failure when the cell is subsequently operating.
On account of the inhomogeneity, of nickel-plated fibrous-structure electrode framework with a width of up to 180 mm, and the even less homogenous edge with a high level of nickel and dendrites which in some cases have been subsequently removed from the surface in a separate working step, single-spot resistance welding is preferred in some regionsxe2x80x94generally in regions around the centre of the weld seam length. But in other regionsxe2x80x94generally starting from one or both edges (outer sides of the fibrous-structure electrode frameworks) resistance-welding achieves improved bonding. Thus, in the latter regions, in the event of transverse forces, the current discharge lug can in some cases be peeled off the fibrous-structure electrode framework over the entire welded area. These circumstances are particularly common when processing relatively thin fibrous-structure electrode frameworks with a nominal thickness of 1.5 mm and with relatively low nickel levels in the fibrous-structure electrode framework.
On account of the abovementioned inhomogeneities in the fibrous-structure electrode framework, regions in which the contact is produced first and at a relatively high pressure (good contact; main welding current path) and regions in which the contact is produced later and at a low pressure (less favorable contact; auxiliary welding current path) are established over the weld seam length during the welding operation, so that it is no longer possible to achieve optimum welding conditions. The welding operation (at the high temperatures which occur) is made more difficult by the melting and evaporating plastics material, which emerges from the nickel-plated fibers.
The best current transfer is achieved at those locations in the weld zone at which the fibrous-structure electrode framework has the highest accumulation of nickel. If there is a non-uniform distribution of the nickel at the reinforced edge on account of the formation of dendrites during the electrodeposition of nickel, it is impossible to achieve a uniform distribution of current over the entire weld length when the current discharge lug is connected to the fibrous-structure electrode framework during a welding operation. This effect is heightened by the non-uniform pressure distribution during the operation of welding an inhomogenous framework edge over the entire weld length.
The welding pressure of the welding electrodes is consumed at those locations in the welding zone at which once again the highest mass accumulation of nickel is present. Thus, it is here that the strongest weld joints are formed. The remaining weld regions are adversely affected, so that in these regions there is only a residual amount of energy available for each welding, and under certain circumstances this energy may even no longer be sufficient to heat the current discharge lug and the fibrous-structure electrode framework in this zone to temperatures above their melting point. These phenomena may be intensified if the welding electrodes are not oriented parallel to one another. Also, the fibrous-structure electrode framework must not slip at the last moment while the welding electrodes are being brought together during the welding operation, and must have a straight edge profile.
If there are crooked and/or curved reinforced edges on the fibrous-structure electrode plates which are separated from the framework strip, single-spot welding to the current discharge lug yields a joint which holds only over a welding width of 70% or even less. Over the remaining 30% or more of the welding width, the upper welding electrode simply fails to include the fibrous-structure electrode framework, since in these regions, on account of the inclination or curvature of the upper edge, it is not in contact with the current discharge lug at all.
It is also possible that, after welding, some of the framework may spring off the current discharge lug, since it has only been adhesively bonded. (There has been no welding of the reinforced edge in this zone on account of the pressure conditions during the single-spot welding having changed.) Fibrous-structure electrodes of this type which have been badly pretreated for the welding operation and provided with a current discharge lug tear when subjected to the loads involved in vibratory filling with active paste, in stripping or in brushing off the paste after the impregnation.
German patent document DE-C 42 25 708 discloses that, on account of a current discharge lug that is formed on the weld-on end of teeth which are spaced apart from one another by teeth spaces, some of the inhomogeneities of the reinforced edge which have been outlined above are evened out (specifically in those regions of the weld length at which tooth gaps lie opposite the fibrous-structure electrode framework). At the other regions of the weld length, at which teeth of the current discharge lug lie opposite the fibrous-structure electrode framework during the welding operation, the inadequacies outlined above apply to the sum of the length of all the teeth sections of the current discharge lug.
Due to the high gradient (that is, a sudden increase/decrease) of the nickel deposition in the edge region in the fibrous-structure electrode framework, there is a high level of scrap involved in resistance welding of the joint between the fibrous-structure electrode framework and the current discharge lug. When the joint between fibrous-structure electrode framework and the current discharge lug is subjected to mechanical loads, such as for example during the vibratory filling with active paste, as is known from the prior art (e.g., from German patent document DE-C 38 22 197), scrap occursxe2x80x94with some of the fibrous-structure electrode frameworks tearing away from the respective welded-on current discharge lugxe2x80x94specifically immediately below the weld zone. Thus, a framework strip of approximately 2 to 5 mm which is secured in the welding bed remains on the current discharge lug over the width of the current discharge lug. Such damage at this preferred location over the lug width is also attributed to the fact that the fibrous-structure electrode framework is weakened, on account of the heating which takes place as a result of the welding operation, with associated local evaporation of the plastics core of the nickel-plated fibers, in addition to being constricted (the cross section being reduced by the welding operation).
Current fibrous-structure framework electrodes, in which, outside the reinforced edge over an area of up to 5 mm, the nickel level is approximately constant over the height of the remaining fibrous-structure electrode framework, apart from undesirable manufacturing fluctuations of the order of magnitude of a few per cent, cannot satisfactorily fulfil the two principal functions demanded of them (namely taking up current from the active compound with minimum possible losses and subsequently carrying current to the current discharge lug). The extent to which they are able to fulfill these functions deteriorates as the operating loads imposed on the storage batteries constructed using these electrodes increase.
This will now be explained in more detail: one of the essential functions of the fibrous-structure electrode framework is to accommodate and hold the active compound in its interior, and to take up the energy which is released in the interior of the fibrous-structure electrode, in the form of a current, as a result of an electrochemical reaction when the storage battery is operating. In the case of storage electrodes, contact between the active compound, which often has a low conductivity, and the nickel-plated fibers of the fibrous-structure electrode framework, which have a good conductivity, must be as intimate as possible, and of a good quality at numerous locations. The porous, three-dimensional structure of the fibrous-structure electrode complies with this requirement.
Another function of the fibrous-structure electrode framework is to carry the current from all regions of the fibrous-structure electrode framework, out of the interior of the electrode, via the electrode current discharge lug, the strap leading to the cell pole, to the outside, with minimum possible losses. That is, it must conduct current just as well from the bottom region as from the middle region or the top region over the entire height of the fibrous-structure electrode. A three-dimensional, highly porous, electrically conductive structure with an approximately constant nickel level over the fibrous-structure electrode height is relatively unsuitable for this function. This adverse property is attributable simply to the design of the fibrous structure, which is generally as homogenous as possible; thus, the conductivity of the metallized fibrous-structure electrode framework is approximately identical in all three directions (the height, the width and the thickness of the framework). The fact that the current discharge lug, in the case of electrodes for storage batteries with prism-shaped housings and relatively large capacities, is preferably situated at the upper edge of the electrode means that the current is preferably carried from the bottom upwards in the electrode. Thus, in statistical terms primarily only this direction of conductivity is used for carrying current in the highly porous fibrous-structure framework. Over this height of the framework, which in low cell types is 160 mm and in high cell types is 240 mm, the conduction of current involves high levels of losses, since the conductivity in the direction under consideration is constant on account of the nickel level of the fibrous-structure framework likewise being constant.
A previously existing reinforced edge is so dimensionally stable that it temporarily inhibits successful performance of, for example, continuous production steps during washing and drying of the framework strips as a whole following the electroplating.
One object of the invention is to provide a metallized fibrous-structure electrode framework and a process for the electroplating of activated and metallized plastic substrates which avoids the drawbacks outlined above, both during production and during the use.
In particular, during the electroplating process a reinforced edge that extends only up to approximately 3 mm into the interior of the electrode framework should not be created; rather a metallized fibrous-structure electrode framework with a nickel level that varies gradually over the electrode height is to be formed during the electroplating by means of suitable internals (diaphragms of particular design) in the electroplating tank. The anodic nickel which was deposited in the previous reinforced edge in the form of dendrites is to be dispensed with.
The creation of fibrous-structure electrode frameworks without dendrites means that dendrites do not have to be removed subsequently in a dedicated operation (thus avoiding the formation of hazardous dusts which are harmful to health, and saving costs). Also, because they are not machined off, they cannot lead to disruptive short circuits when the cell is operating. A particular design of the internals in the electroplating tank is to ensure only one premetallized fibrous-structure web has to be inserted into the stand frames, secured, removed after the electroplating process, centrifuged and washed, and this web is then cut, stamped or divided in some other way into identical fibrous-structure electrode framework blanks over the height and width of the web.
Another object of the invention is to provide a fibrous-structure electrode framework which, for use in a storage battery, has a lower nickel level in its lower region than in its middle region, and the highest nickel level in its upper region (the zone in which it is subsequently welded to the current discharge lug), so as to ensure suitable conductivity for the active compound over all regions of the electrodes, as seen over the height (in total), and so that the current can be carried to the current discharge lug with relatively low losses.
In addition, the entire web, at those regions in which it is subsequently divided into the individual fibrous-structure framework strips, is equipped over a relatively large region with a constant nickel level. Thus, during such division, correctly dimensioned, straight edges are always formed in the fibrous-structure framework plates before the current discharge lug is welded on, with the upper edge and lower edge, and also the right-hand and left-hand edges of the fibrous-structure electrode framework running parallel to one another, and with the upper and lower edges running at right angles to the side end edges.
Another important object of the invention is to provide, in the upper region, a zone with a nickel level that is sufficiently high it is possible to reduce the scrap rates when the fibrous-structure electrode frameworks are welded to the current discharge lugs. In this context, it is necessary to achieve a high nickel level even in the interior of the fibrous-structure framework and over a zone extending from its upper weld-on edge which is advantageously longer than the weld-on zone, so that weakening of this zone caused by evaporation of the plastic cores of the nickel-plated fibers during the welding operation can be compensated for compared to the prior art, through connection of the fibrous-structure electrode framework to the current discharge lug.
Another object is to produce a nickel level, over the entire height, width and thickness of the fibrous-structure electrode framework and particularly, in the bottom region of the framework (the zone with the lowest nickel level of the fibrous-structure electrode framework), which is sufficiently high that the framework, even in bottom region, is strong enough to withstand the paste pressure which exists during the filling with a pasty, active compound, by whatever method (vibratory shaking, rolling-in or pressing-in with simultaneous calibration of the framework), such that the paste penetrates into the pores without problems and with simultaneous displacement of the air therein and does not compress and compact the fibrous-structure electrode framework in the manner of a sponge during the filling operation when it is pressed out.
A further object of the invention is to fabricate a fibrous-structure electrode framework from metallized plastic fibers with welded-on, thick current discharge lug comprising teeth which are spaced apart from one another by teeth spaces, in which i) there is no cracking in the fibrous-structure electrode framework in the vicinity of the weld joint, ii) the fibrous-structure electrode framework does not have to be stamped in the welding region prior to the welding, and iii) over all partial sections of the welding length (sum of the teeth widths at the level of the welding-on line) there are uniform pressure distribution and uniform current distribution during the welding, and contact regions and contacts which are always identical are created at regular intervals.
The weld joint is to be achievable using single-spot welding over a fibrous-structure electrode framework width of up to 200 mm and is to have scrap rates during the welding operation of below 1% even for thin frameworks (1.5 mm nominal thickness). The weld joint between the fibrous-structure electrode framework according to the invention and the current discharge lug is to have a high strength (not only under tensile load but also in the transverse direction, and not only in preferred weld regions but also in the edge zones). This enables fibrous-structure electrodes with welded-on current discharge lugs to be produced with favourable electrical contact resistances and high service lives, so that they can be used not only in storage batteries in stationary installations, but also in industrial trucks or underground trains or similar applications involving vibrating loads.
These and other objects and advantages are achieved by the invention, in which the activation and chemical metallization of the plastics frameworks (in particular felts, needled felts or nonwovens) is in practice carried out using known techniques. Suitable materials for the fibers include the plastics materials which are also suitable for textile substrates, e.g., polyolefins, polyamides, poly-acrylonitrile, etc., provided that they are stable with respect to the electrolyte.
The procedure indicated can be used in particular for the electroplating of pretreated structure webs made from nonwoven or needled felt which have a web thickness of from 0.25 mm to 5.00 mm, a porosity of the untreated web of from 50% to 98%, and a basis weight of the untreated web of from 50 g/m2 to 800 g/m2, the plastics fibers of the web having a diameter from 0.7 dtex to 7.9 dtex, with a staple length of the plastics fibers of from 15 mm to 80 mm. The electroplating operation is preferably carried out until the structure webs have been coated with a layer of nickel or copper of on average from 50 mg metal/cm2 to 300 mg metal/cm2.
According to the invention, following the production of a cohesive, premetallized fibrous-structure framework web, without prior cutting of strips to electrode height, the entire web is clamped into electroplating stands. It is then introduced into the electrolyte bath, and reinforced by electrodeposition in the bath. During the electrodeposition of metal, a rigid diaphragm system is introduced between each of the anodes and the premetallized fibrous-structure framework web (which is connected as cathode). Taking into account the electroplating bath dimensions, the introduction of the diaphragm system leads to alternating formation of strips with a graduated nickel level over the height of the web, with the strip height corresponding to the subsequent fibrous-structure electrode framework height. Each strip has a zone with a high, medium and low nickel level.
After completion of electrodeposition and removal of the electrolyte from the pores of the fibrous-structure electrode framework web, it is cut to size (to electrode height) in such a manner as to create strips, each of which extends (heightwise) from a zone with the highest through a zone with the lowest nickel level. The strips are subsequently separated into electrode width.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.